The present invention relates to rechargeable battery cell units which can be interconnected to form a battery module, and particularly to an intrinsically-safe battery cell unit comprising a switch-on delay and a switching method for intrinsically-safe battery cells.
High-performance rechargeable battery modules, typically consisting of a plurality of battery cells electrically connected to one another, are an important component of the electric and hybrid vehicle technology. Particularly the requirements for performance and safety of battery systems, which can consist of a plurality of battery modules interconnected with one another and therefore a relatively high number of battery cells, belong to the challenges of the development of storage battery technologies. Lithium-ion cells are increasingly used in the automobile industry. Lithium-ion batteries are however relatively sensitive with regard to overcharging as well as deep discharging.
In order to increase the reliability primarily of lithium-ion batteries, intrinsically-safe battery cells and battery modules are desirable, which can protect themselves from inadmissible electrical operating conditions by means of the electronics associated therewith, without being dependent on the function of electronics of a battery management system. Intrinsically-safe battery cells should be short-circuit proof, non-combustible and non-explosive and also not trigger any exothermal reactions, in English language usage also known as “thermal runaway”. Intrinsically-safe battery cells are known, for example, from the prior art, which have electronic components, such as, for example, an ultrafast discharge circuit which protects the battery from breakdowns, such as internal or external short circuits, overloading, deep discharge or inadmissible external heating.
In order to achieve a certain value of the total voltage of a battery module or a battery system according to the current prior art, a plurality of electrically intrinsically-safe battery cells, which are either connected in series and/or in parallel with one another, are switched on by a superordinate control unit, for example a battery management system, corresponding to a predetermined probability. In order to maximize the performance of the individual battery cells and to increase the service life thereof, the individual battery cells are equipped with electronics in order to determine the intrinsic state conditions and to accordingly carry out an intrinsic switching state. The prioritization of the use of the battery cells typically occurs either according to the charge state of the individual battery cells, also denoted in English language usage as state of charge (SOC), or according to the ageing of individual battery cells, which is denoted as state of health (SOH) in the English language usage. In order to implement this switching method, each individual battery cell, according to the prior art, is equipped with a microprocessor unit, which in English language usage is also referred to as a micro-control unit (MCU), which determines the switching probability of the corresponding battery cell. This requires significant technical effort and expense and furthermore stresses the battery management system and in particular the information density of the communication bus.
The American patent application US 2012/0274140A1 discloses a battery system which has a switching device that is connected to a control unit. The switching device comprises a plurality of battery cells and a wiring which allows the control unit to change the configuration of the individual battery cells in the battery module. In so doing, the state of charge and the ageing of the individual battery cells, the past history of the battery module as well as environmental conditions and manufacturing specifications can be taken into account. With the aid of the switching device, the output voltage of the battery module can be adapted to the requirements of a consumer, for example an electric motor.
The switching methods for battery cells or battery modules known from the prior art have a relatively high complexity, which impairs the efficiency and leads to a strong utilization of the communication bus between the individual battery cells and the battery management system. An overloading of the communication bus can result in delays when switching on and off the battery cells of a battery module or battery system. As a result, the accuracy of the control for setting a certain nominal voltage can be impaired.
In front of this background, it is an aim of the present invention to improve the switching capacity of intrinsically-safe battery cells, in particular of lithium-ion battery cells, in particular with regard to the reduction in the complexity of the battery module or battery system with regard to the information load on the communication bus between the individual battery cells and the battery management system.